1. Field of the Invention
The present invention is related to gate structures of a CMOS device and a method for manufacturing the same, and particularly to a method to increase the work function of a work function modulation layer of the gate structure of the CMOS device by means of nitrogen doping process.
2. Description of the Prior Art
With the development of semiconductor technology and the increasing density of the devices, the complementary metal oxide semiconductor (CMOS) devices having characteristic of low energy consumption is broadly used in the integrated circuits.
Conventional polysilicon gate structure having a gate dielectric layer of SiO2, and a conductive layer of polysilicon and WSi encounters a problem of size reduction during the tendency of miniaturizing the size of the device having the conventional polysilicon gate. Several materials are developed to be used in the gate structure, such as the dual work function metals, which are used to replace the conventional polysilicon layer in the gate structure. Conventional gate structures of the CMOS device have a work function metal for the gate structure of the NMOS device and another work function metal for the PMOS device. During the process of forming the conventional gate structures of the CMOS device, tantalum layer for the PMOS device is blanketly deposited. A portion of the tantalum layer disposed on the NMOS device is removed, and a ruthenium layer for the NMOS device is blanketly deposited. Then, the ruthenium layer disposed on the PMOS is removed. Accordingly, the formation of the conventional gate structures of the CMOS requires at least two deposition processes and two removing processes for forming a corresponding work function metal on the PMOS device or the NMOS device. Therefore, the manufacturing process for forming the gate structures of the CMOS device is complicated.
Therefore, the semiconductor technology is developed to simplify the manufacturing process for forming the gate structures of the CMOS device and to form the gate structures with high performance.